Gephart Raymond T, Williams Neil J, Reibenspies Joseph H, De Sousa Alvaro S, Hancock Robert D
Department of Chemistry and Biochemistry, University of North Carolina at Wilmington, Wilmington, North Carolina 28403, USA.
Inorg Chem. 2009 Sep 7;48(17):8201-9. doi: 10.1021/ic900650d.
The metal ion selectivity for M(III) (M = metal) ions exhibited by the highly preorganized ligand PDALC is investigated (PDALC = 2,9-bis(hydroxymethyl)-1,10-phenanthroline). The structures are reported of [Bi(PDALC)(H(2)O)(2)(ClO(4))(3)] x H(2)O (1), monoclinic, P2(1)/c, a = 12.8140(17), b = 19.242(3), c = 9.2917(12) A, beta = 91.763(2) degrees, V = 2289.9(5) A(3), Z = 4, R = 0.0428; [Th(PDALC)(NO(3))(4)] x 3 H(2)O (2), monoclinic, P2(1)/n, a = 7.876(3), b = 22.827(9), c = 12.324(5) A, beta = 94.651(6) degrees, V = 2208.4(15) A(3), Z = 4, R = 0.0669; Cd(PDALC)(2)(2) (3)), triclinic, P1, a = 7.5871(16), b = 13.884(3), c = 14.618(3) A, alpha = 74.081(2) degrees, beta = 88.422(2) degrees, gamma = 78.454(2) degrees, V = 1450.2(5) A(3), Z = 2, R = 0.0267. The Bi in 1 is best regarded as 9-coordinate, with four short bonds to the PDALC, and two short bonds to the coordinated water molecules, with three long bonds to perchlorate oxygens. The Bi-N bonds at 2.35 A are by a considerable margin the shortest Bi-N bonds to 1,10-phenanthroline (phen) type ligands, which is suggested to be due to the Bi adapting to the metal ion size requirements of PDALC. The Th(IV) in 2 is 12-coordinate, with four bonds to PDALC, and the four chelated nitrates, with close to normal bond lengths to the PDALC ligand. The Cd(II) in 3 is 8-coordinate, with Cd-N and Cd-O bonds that are similar to those found in other 8-coordinate Cd(II) complexes. The five known structures of PDALC complexes, including the three reported here, suggest that the M-N bonds to PDALC are quite easily varied in length in response to differing metal ion sizes, but that the M-O bonds are more constrained by the rigid ligand to be close to the ideal value of 2.50 A. The formation constants (log K(1)) for M(III) ions with PDALC show that for small metal ions such as Ga(III) and Fe(III), log K(1) is only slightly higher than for phen, suggesting that these metal ions are too small to coordinate to the alcoholic oxygen donors of PDALC. For larger metal ions such as Bi(III), Gd(III), Th(IV), and UO(2)(2+), log K(1) for PDALC is higher than log K(1) for phen by more than 5 log units, which stabilization is attributed to the fact that PDALC is preorganized for complexation with large metal ions with an ionic radius of about 1.0 A. The fluorescence of M(III) complexes of PDALC is discussed. PDALC free ligand gives fluorescence typical of phen ligands, with the protonated form giving a broad less intense band, and the non-protonated form of the ligand giving an intense structured set of bands. Large lanthanide ions without partially filled f-subshells, such as La(III), Lu(III), and also Y(III), give a fairly strong CHEF (chelation-enhanced fluorescence) effect, while those with partially filled f-subshells, such as Gd(III), Yb(III), and Tb(III), strongly quench the fluorescence of PDALC. A heavy element such as Bi(III) has strong spin-orbit coupling effects that act to quench the fluorescence of PDALC almost completely, which effect is enhanced by the covalence of the Bi-N bonds.
研究了高度预组织化的配体PDALC（PDALC = 2,9 - 双（羟甲基）- 1,10 - 菲咯啉）对M(III)（M = 金属）离子的金属离子选择性。报道了[Bi(PDALC)(H₂O)₂(ClO₄)₃]·H₂O（1）的结构，单斜晶系，P2₁/c，a = 12.8140(17)，b = 19.242(3)，c = 9.2917(12) Å，β = 91.763(2)°，V = 2289.9(5) ų，Z = 4，R = 0.0428；[Th(PDALC)(NO₃)₄]·3H₂O（2）的结构，单斜晶系，P2₁/n，a = 7.876(3)，b = 22.827(9)，c = 12.324(5) Å，β = 94.651(6)°，V = 2208.4(15) ų，Z = 4，R = 0.0669；Cd(PDALC)₂₂（3）的结构，三斜晶系，P1，a = 7.5871(16)，b = 13.884(3)，c = 14.618(3) Å，α = 74.081(2)°，β = 88.422(2)°，γ = 78.454(2)°，V = 1450.2(5) ų，Z = 2，R = 0.0267。1中的Bi最好看作是九配位，与PDALC有四条短键，与配位水分子有两条短键，与高氯酸根氧有三条长键。2.35 Å的Bi - N键比与1,10 - 菲咯啉（phen）型配体形成的Bi - N键短得多，这表明是由于Bi适应了PDALC的金属离子尺寸要求。2中的Th(IV)是十二配位,与PDALC有四条键，与四个螯合的硝酸盐有键，与PDALC配体的键长接近正常。3中的Cd(II)是八配位，Cd - N和Cd - O键与其他八配位Cd(II)配合物中的键相似。包括此处报道的三个在内的PDALC配合物的五个已知结构表明，与PDALC的M - N键长度很容易因不同的金属离子尺寸而变化，但M - O键更受刚性配体的限制，接近2.50 Å的理想值。M(III)离子与PDALC的形成常数（log K₁）表明，对于诸如Ga(III)和Fe(III)等小金属离子，log K₁仅比与phen的略高，这表明这些金属离子太小，无法与PDALC的醇式氧供体配位。对于诸如Bi(III)、Gd(III)、Th(IV)和UO₂²⁺等较大金属离子，PDALC的log K₁比phen的log K₁高5个以上对数单位，这种稳定性归因于PDALC预组织用于与离子半径约为1.0 Å的大金属离子络合。讨论了PDALC的M(III)配合物的荧光。游离的PDALC配体发出典型的phen配体荧光，质子化形式给出较宽且强度较低的谱带，配体的非质子化形式给出一组强烈的结构化谱带。没有部分填充f亚壳层的大镧系离子，如La(III)、Lu(III)以及Y(III)，产生相当强的螯合增强荧光（CHEF）效应，而那些具有部分填充f亚壳层的离子，如Gd(III)、Yb(III)和Tb(III)，强烈淬灭PDALC的荧光。像Bi(III)这样的重元素具有很强的自旋 - 轨道耦合效应，几乎完全淬灭PDALC的荧光，这种效应因Bi - N键的共价性而增强。
